Shell to be driven into a bone substance for a prosthetic joint

Abstract

A shell (1) for a prosthetic joint to be driven into a bone substance. The shell having an outer lateral surface (4) which is convexly curved in cross section and on which a plurality of ribs (5) is arranged. All ribs extend in the same direction at a preferably increasing gradient angle of 45° to 85° at the equatorial end (6) to a pole-side end (7). The cumulative flank projection area of all ribs (5) corresponds to at least a fifth of the entire outer lateral surface. As a result of this measure, a very high primary stability is achieved once the shell has been driven in, the shell being screwed into the bone substance very precisely and without bone material being sheared off. This arrangement can also be applied, similarly, to a concavely curved inner lateral surface.

The invention claimed is: 
     
       1. A shell to be driven into a bone substance for a prosthetic joint,
 having an outer lateral surface which is convexly curved, in cross-section, or 
 having an inner lateral surface which is convexly curved, 
 on which outer or inner lateral surface there is arranged a plurality of ribs, 
 wherein all ribs extend in the same direction under a pitch angle from 45° to 85° at the equatorial end toward a pole-sided end on the outer lateral surface or on the inner lateral surface, and 
 each rib has a flank projection area based on a plane running through a longitudinal extent of the rib and perpendicularly to the outer lateral surface or to the inner lateral surface, and a sum of the flank projection area of all ribs corresponds to at least one fifth of the entire outer lateral surface or the entire inner lateral surface. 
 
     
     
       2. The shell as claimed in  claim 1 , wherein said outer lateral surface or said inner lateral surface is spherical. 
     
     
       3. The shell as claimed in  claim 1 , wherein said pitch angle increases from the equatorial end toward the pole-sided end. 
     
     
       4. The shell as claimed in  claim 1 , wherein the ratio between the sum of the flank projection area of all ribs and the outer lateral surface or the inner lateral surface is in the range from 0.2:1 to 1:1. 
     
     
       5. The shell as claimed in  claim 1 , wherein at least 20 ribs are arranged on the outer lateral surface or on the inner lateral surface. 
     
     
       6. The shell as claimed in  claim 1 , wherein between 30 and 80 ribs are arranged on the outer lateral surface or on the inner lateral surface. 
     
     
       7. The shell as claimed in  claim 1 , wherein an interval between adjacent ribs, at the equatorial end from rib center to rib center on the outer lateral surface or on the inner lateral surface, is in the range from 0.2 mm to 4 mm. 
     
     
       8. The shell as claimed in  claim 1 , wherein at least 30% of the ribs extend over more than half a height of the shell, based on the longitudinal central axis thereof. 
     
     
       9. The shell as claimed in  claim 1 , wherein at least 50% of the ribs extend over more than half a height of the shell, based on the longitudinal central axis thereof. 
     
     
       10. The shell as claimed in  claim 1 , wherein ribs of differing length are arranged on the outer lateral surface or on the inner lateral surface. 
     
     
       11. The shell as claimed in  claim 10 , wherein the ribs of differing length are arranged in a regular sequence. 
     
     
       12. The shell as claimed in  claim 1 , wherein a rib height from a rib foundation to a rib vertex is in the range from 0.1 mm to 4 mm. 
     
     
       13. The shell as claimed in  1 , wherein ribs of differing rib height are arranged on the outer lateral surface or on the inner lateral surface. 
     
     
       14. The shell as claimed in  13 , wherein the ribs of differing rib height are arranged in a regular sequence. 
     
     
       15. The shell as claimed in  claim 1 , wherein ribs of differing rib height are arranged on a certain latitude based on a circumference of the outer lateral surface or the inner lateral surface. 
     
     
       16. The shell as claimed in  claim 1 , wherein the ribs have a cross-section which tapers from a rib foundation toward a rib vertex, based on a plane running perpendicularly to a longitudinal extent of the rib and perpendicularly to the outer lateral surface or to the inner lateral surface. 
     
     
       17. The shell as claimed in  claim 16 , wherein the ribs have a wedge-shaped cross-section. 
     
     
       18. The shell as claimed in  claim 1 , wherein opposing flank surfaces of the individual ribs have different roughness values such that the flanks subjected to a greater load during drive-in have a lower roughness value than the flanks subjected to a greater load during pull-out. 
     
     
       19. The shell as claimed in  claim 1 , wherein at least some of the ribs are interrupted to form individual rib teeth. 
     
     
       20. The shell as claimed in  claim 19 , wherein the rib teeth of a rib have a differing configuration between an equatorial end and a pole-sided end. 
     
     
       21. The shell as claimed in  claim 19 , wherein the rib teeth form irregular, multisurface bodies having a quadrangular footprint, two flank sides inclined against one another, a pole side facing the pole, and an equator side facing the equator. 
     
     
       22. The shell as claimed in  claim 20 , wherein the successive rib teeth of a rib are configured such that displacement of bone material takes place in a drive-in direction and an anchoring in the bone material takes place in a screw-out direction. 
     
     
       23. The shell as claimed in  claim 19 , wherein the gaps between the rib teeth do not extend as far as the outer lateral surface or the inner lateral surface. 
     
     
       24. The shell as claimed in  claim 1 , wherein at least one of said outer lateral surface or said inner lateral surface and the ribs is fully or partially provided with an osteoinductive coating. 
     
     
       25. The shell as claimed in  claim 1 , wherein the shell is a joint shell for a prosthetic hip joint to be driven into an acetabulum, and a ratio between the sum of the flank projection area of all ribs and the outer lateral surface is in the range from 0.2:1 to 0.8:1. 
     
     
       26. The shell as claimed in  claim 1 , wherein the shell is a humeral anchor to be driven into a humerus, and a ratio between the sum of the flank projection area of all ribs and the outer lateral surface is in the range from 0.3:1 to 1:1. 
     
     
       27. The shell as claimed in  claim 1 , wherein a course of the ribs is chosen such that each rotation by a predetermined angular value brings about a constant advance of the shell.